The present invention relates generally to magnetic recording tape guide assemblies, and more particularly, to a compact tape guide assembly which provides minimized lateral tape motion without tape damage.
Magnetic media are used for storage of data generated by computers. Typically a magnetic medium is presented to a magnetic head which ordinarily can either read or write data on the medium. Magnetic storage disks, commonly referred to as hard disks, are presently the preferred storage medium for use in computer systems where fast access time and substantial storage capacity are of interest. However, because of their low cost, portability, compactness and storage capacity, magnetic tapes are also used for data storage.
One advantage which tapes have over hard disks is that once the data is on a magnetic tape, the tape and its container (commonly referred to as a cartridge) can be removed from the computer and stored in a secure location or can be used for carrying or mailing data to a remote location. This removable feature allows tape and tape drives to be used as archival storage and/or "back-up" systems for hard disks. However, the data error rate must be quite low to allow use as archival and/or backup storage devices.
In order to increase storage density for a given cartridge size, thinner tape may be employed. One popular tape drive assembly, known generally as a five and one quarter inch (i.e., 51/4") tape drive, is typically five and three quarters inch wide by three and one quarter inches high by nine inches deep (i.e., 53/4".times.31/4".times.9"). This drive typically receives a five and one quarter inch cartridge which is about four and one tenth inches square and one inch high. Typically, six hundred feet of one half inch wide, one millinch thick (i.e., 1 mil) tape is wound onto a three and six tenth inch diameter supply reel in a five and one quarter inch cartridge for data storage use in a five and one quarter inch tape drive. The storage capacity of a five and one quarter inch cartridge, however, can be increased by lengthening the tape. For example, approximately one thousand, one hundred feet of one half millinch thick tape may be loaded onto the same supply reel. Therefore, more data may be stored in a five and one quarter inch cartridge using one half millinch thick tape versus one millinch thick tape.
Another way to increase the storage density for a given cartridge size is to write the bits on the tape in smaller areas and on a plurality of parallel longitudinal tracks. As more tracks are recorded on a tape, each track then becomes narrower and the tape must now be constrained from shifting up or down (called lateral tape motion) in a direction perpendicular to the tape travel path as the tape passes by the magnetic head in order to maintain proper alignment of the head and tracks on the tape. Constraining the tape to minimize lateral tape motion prevents data retrieval errors.
Lateral tape motion is defined as the peak-to-peak distance of the undesirable movement (in-plane) of the tape perpendicular to its prescribed longitudinal direction of motion past the head. Lateral tape motion is a major limiting factor in determining the minimum width of a track and the minimum spacing between tracks on the tape. Thus, as lateral tape motion is reduced, more tracks may be stored on the tape and the tape density increases accordingly.
One concern with reducing lateral tape motion is the possible damage to the tape due to wear from the tape drive assembly. As tape thickness is reduced in order to store more data in a particular sized cartridge, the strength of the tape is similarly reduced. Thus, the possibility of damage to the tape due to wear increases.
A prior art tape guide assembly is described in U.S. Pat. No. 5,173,828, entitled "Compact Multiple Roller Tape Guide Assembly", by Andrew E. Tanzer, et. al., and is assigned to the same assignee as the present invention. The tape guide assembly described in U.S. Pat. No. 5,173,828 includes six tape rollers R1-R6. FIG. 1 shows the arrangement of three of the six rollers, R1-R3, in a cross sectional view of the tape guide assembly of U.S. Pat. No. 5,173,828.
Essentially, each tape guide roller is a machined cylinder. Each roller includes a stem 20, a tape support surface 22, and flanges 24, 26. The tape support surface 22 is uniformly flat, extending parallel to the roller shaft axis 28, and preferably lies on the circumference of a six tenths millinch diameter D. The roller is mounted on a preloaded ball bearing (not shown) to prevent roller movement lateral to the tape. A small coil spring 30 and washer 32 are used to preload the roller and bearing assembly.
In the roller guide assembly of U.S. Pat. No. 5,173,828, the rollers rotate with the tape in the direction of tape travel as the tape advances. The flanges 24, 26 have surfaces 24a, 26a which may contact and provide guidance for the longitudinal edges of the tape as the tape advances along the tape travel path. When a tape edge comes in contact with a flange surface 24a or 26a, there is very little friction between the tape edge and the flange surface, because the flange is fixed to the roller so that the flanges 24, 26 and flange surfaces 24a, 26a rotate with the tape as it advances.
The distance between the flange surfaces 24a, 26a is greater than the width of the tape. Thus, the flange surfaces 24a, 26a are not in constant contact with the longitudinal tape edges. This permits a window of lateral tape movement equal to the distance between the flange surfaces 24a, 26a minus the tape width. The width of the window directly affects the thickness of the track width, the spacing between tracks and the distance from each longitudinal tape edge where the first track may be stored.
Another prior art technique for reducing or minimizing lateral tape motion is to provide a first fixed plurality of tabs having a surface for contact with a first longitudinal tape edge and a second corresponding plurality of tabs having a surface for contact with the second longitudinal tape edge where the second plurality of tabs is flexible in the direction perpendicular to the tape travel path. With such an arrangement, the second plurality of tabs causes the first longitudinal tape edge to remain in contact with the first plurality of tabs while compensating for variations in tape width.
One concern with such an arrangement is tape edge damage due to wear. Because both tape edges remain in substantially constant contact with the surfaces of both pluralities of tabs, as the tape advances, the tape edges pass across the fixed surfaces (i.e., the surfaces do not move in the tape travel direction) and damage due to friction with these surfaces may result.